1. Technical Field
The present invention relates to a method for manufacturing single-crystal silicon, and particularly to a method for manufacturing single-crystal silicon manufactured by a Czochralski method.
2. Description of the Related Art
The Czochralski method has been widely used in the manufacture of single-crystal silicon. In the Czochralski method, a polycrystalline material is melted in a quartz crucible, and a seed crystal is brought into contact with a material melt and is pulled up, thereby growing the single-crystal silicon.
Dislocation of the single-crystal silicon occurs in some cases during growth of the single-crystal silicon. It is pointed out that one of the reasons for dislocation of the single-crystal silicon is that cristobalite precipitated on an inner surface of the crucible made of quartz glass is released into the silicon melt and the cristobalite is taken into a silicon ingot when the silicon is pulled up.
Japanese Patent Laid-Open Application No. 9-110590 describes a method for promoting crystallization of quartz and preventing release of cristobalite by adhering a devitrification promoter containing an alkaline-earth metal such as barium to an inner surface of a quartz crucible.
Japanese Patent Laid-Open Application No. 2003-160393 describes a method for reducing the occurrence of dislocations during growth of single-crystal silicon by decreasing the concentration of a devitrification promoter, which is adhered to an inner surface of a quartz crucible, at a portion where the temperature during pulling-up of the single-crystal silicon is high, and increasing the concentration of the devitrification promoter at a portion where the temperature is low.
In recent years, single-crystal silicon has been manufactured using a multi-pulling method for pulling up a plurality of pieces of single-crystal silicon from a material melt in an identical crucible. According to this method, a single crystal is pulled up from the material melt, and then, a polycrystalline material is additionally charged into and melted in the remaining material melt without turning off a heater, and then, a next single crystal is pulled up. By repeating these steps of additionally charging the polycrystalline material into the material melt, melting the polycrystalline material in the material melt, and then pulling up a next single crystal, a plurality of pieces of single-crystal silicon are pulled up using the identical crucible.
When a plurality of silicon single crystals are pulled up in the identical crucible using the above-mentioned multi-pulling method, the operation takes a long time, and thus, the crucible is also exposed to high temperature for a long time. Even if a crucible having a devitrification promoter containing barium adhered thereto is used in the manufacture of the single-crystal silicon by the multi-pulling method, dislocations occur in some cases when the single-crystal silicon is separated from the material melt.